To learn how neurophysiological taste responses in the central nervous system of the rat change during development, single-cell responses to stimulation of the tongue with salts, acids, sugars, quinine and amino acids will be recorded in the rat nucleus of the solitary tract (NTS), pontine taste area (PTA) and lateral hypothalamic area (LHA). Rats aged 1-20 days of age, 25-35 days of age and adults (60-100 days of age) will be studied. The three brain areas chosen for investigation are first-, second- and third-order relays in the gustatory pathway. These have been implicated as having different functional importance for taste-related behaviors in the adult rat. For example, the NTS and PTA may be neural substrates for taste hedonics whereas the LHA is an area in which taste information may be used in integrative processes such as feeding. The proposed studies will provide new information on: 1) when taste responses can first be recorded in the NTS, PTA and LHA, 2) how and when taste response characteristics change at each synaptic level throughout the rat's development; and 3) how the neural taste message changes across synapses at each age. Findings may then be compared with existing knowledge of the development of taste preferences and aversions and the development of feeding to clarify the contribution of each nucleus to these behaviors. Comparisons of developmental changes among the three brain areas may enable identificaton of "critical periods" for taste which will aid in understanding the origin and mechanisms of sweet and salt preferences. Thus, these results provide new information on the development of central nervous system taste responses that relate to development of taste preferences and aversions.